Super fun bullet hellek game with birds!
few suggestions. Not sure if its possible or how you do it within unity, but going full screen is really not needed for a game like this. Maxing out at a scale of x4 of the game would have been really nice. This way you can still get the close box so you can quit the game. Along with that, if you do decide to keep your games full screen, having an exit button would be super helpful so i don't have to force close it. Or maybe starting off in windowed mode then giving the option to go full screen.
the way you did your background scrolling was a bit of an odd design choice. I know your going for the retro Gameboy scanline approach for how the level was scrolling down but honestly i think that it took away a lot from this at least for me. "well at least in fullscreen mode on a 37" monitor" Its a bit hard on the eyes when the movement of your body, bullets and all the other moving objects are at 60fps but your background is rendering at 10fps. I think that's how I can best explain it.
I think if the background had a smooth scroll to it, it would have looked less of that ultra retro feel but i think it would have improved the project overall. And I know this is a hard thing to try to emulate on modern screens but something we should consider.
something to think about, honestly i would almost like to play a version that had a smoothed out background just so i can play it longer without getting that visual headack.
Great job overall!